The present invention relates to a support for a natural human heart which may be used for the surgical correction of a deformed heart valve, and in particular a dilated heart valve.
The human heart generally includes four valves with the more critical of these valves being the tricuspid valve. The tricuspid valve is located in the right atrioventricular opening. The other important valve is the mitral valve which is located in the left atrioventricular opening. Both of these valves are intended to prevent regurgitation of blood from the ventricle into the atrium when the ventricle contracts. In preventing blood regurgitation, both valves must be able to withstand considerable back pressure as the ventricle contracts. The valve cusps are anchored to the muscular wall of the heart by delicate but strong fibrous cords in order to support the cusps during ventricular contraction. Furthermore, the geometry of the heart valves ensures that the cusps overlie each other to assist in controlling the regurgitation of the blood during ventricular contraction.
Diseases and certain natural defects to heart valves can impair the functioning of the cusps in preventing regurgitation. For example, certain diseases cause the dilation of the heart valve annulus. This dilation results in the distortion of the valve geometry or shape displacing one or more of the valve cusps from the center of the valve. The displacement of the cusps away from the center of the valve results in an ineffective closure of the valve during ventricular contraction. This results in the regurgitation or leakage of blood during ventricle contraction. Diseases such as rheumatic fever or bacterial inflammations of the heart tissue can cause distortion or dilation of the valvular annulus. Other diseases or malformations may result in the distortion of the cusps.
One method of repairing impaired valves is the complete surgical replacement of the valve. This method is particularly suitable when one of the cusps has been severely damaged or deformed. However, presently available artificial heart valves are not as durable as natural heart valves, and it is usually more preferable if the patient's heart valve can be left intact.
While it is difficult to retain a valve with diseased or deformed cusps, presently practiced methods provide for the ability to surgically correct dilated valve annulus. In view of the durability factor with artificial valves it is desirable to save the valve instead of performing a complete replacement.
These techniques for repairing dilated or elongated valve annulus are generally known as annuloplasty which is a surgical procedure for constraining the valve annulus dilation. In this procedure a prosthesis is sutured about the base of the valve leaflets to restrict the dilated valve annulus. The prosthesis restricts the movement of the valve annulus during the opening and closing of the valve. Prostheses used in annuloplasty are designed to provide sufficient rigidity to adequately support the valve annulus in an effort to facilitate the healing of the valve annulus, while also providing sufficient flexibility to resemble, as close as possible, the natural movement of the valve annulus during the opening and closing of the valve. This is particularly important since prosthesis are normally retained, even after the healing of the valve annulus.
Over the years different types of prostheses have been developed for use in annuloplasty surgery. In general prosthesis are annular or partially annular shaped members which fit about the base of the valve annulus against the leaflets. Initially, the prostheses were designed as rigid frame members. The initial concern was to develop a prosthesis which significantly restricted the dilation of the valve annulus. These annular prostheses were formed from a metallic or other rigid material, which flexes little, if at all, during the normal opening and closing of the valve. Examples of rigid annuloplasty ring prosthesis are disclosed in U.S. Pat. Nos. 3,656,185, issued to Carpentier on Apr. 18, 1972; and 4,164,046, issued to Cooley on Aug. 14, 1979.
Certain artificial heart valves have also been developed with rigid frame members having a rigidity similar to the rigidity of the described valve prosthesis. Examples of this type of heart valve are disclosed in U.S. Pat. Nos. 4,204,283, issued to Bellhouse et al on May 27, 1980; and 4,306,319, issued to Kaster on Dec. 22, 1981.
As stated, a rigid annuloplasty ring prosthesis adequately restricts valve dilation to promote the healing of the valve annulus. However, this rigidity prevents the normal flexibility of the valve annulus. That is, a normal heart valve annulus continuously flexes during the cardiac cycle, and a rigid ring prosthesis interferes with this movement. Since it is standard to retain the prosthesis, even after the valve annulus has healed, the rigidity of the prosthesis will permanently impair the functioning of the valve. Another disadvantage with a rigid ring prosthesis is the tendency for the sutures to become torn loose during the normal movement of the valve annulus.
Other workers have suggested the use of completely flexible annuloplasty ring prosthesis, in order to overcome the disadvantages of rigid ring prosthesis. This type of prosthesis is formed with a cloth or other very flexible material frame member. The resulting prosthesis provides little, if any resistance to the dilation of the annulus during the opening and closing of the valve. While these types of annuloplasty ring prosthesis offer increased flexibility, such prosthesis fail to correct that valve disfunction due to the dilation of the valve annulus.
Examples of completely flexible ring prosthesis are disclosed in U.S. Pat. No. 4,290,151, issued to Massana on Sept. 22, 1981, and are discussed in the articles of Carlos D. Duran and Jose Luis M. Ubago, "Clinical and Hemodymanic Performance of a Totally Flexible Prosethetic Ring for Atrioventricular Valve Reconstruction", 5 Annals of Thoracic Surgery, (No. 5), 458-463, (November 1976) and M. Puig Massana et al, "Conservative Surgery of the Mitral Valve Annuloplasty on a New AdJustable Ring", Cardiovascular Surgery 1980, 30-37, (1981).
Still other workers have suggested annuloplasty ring prosthesis which are adjustable, either during the surgical implantation, or as the ring prosthesis during the opening and closing of the valve. This type of adjustable prosthesis is typically designed in combination with a rigid, or at least partially rigid frame member. For example, the ring prosthesis taught in U.S. Pat. No. 4,489,446, issued to Reed on Dec. 25, 1984, allows for self adJustment of the prosthesis annulus by constructing the valve frame member as two reciprocating pieces. However, while the resulting prosthesis self adjusts in at least one direction, the individual frame members are formed from a rigid material. Thus the prosthesis suffers the same disadvantages as the above discussed rigid ring prosthesis.
Other examples of adjustable ring prosthesis are taught in U.S. Pat. Nos. 4,602,911, issued to Ahmadi et al and 4,042,979, issued to Angell on Aug. 23, 1977, provide for mechanism of adjusting the ring circumference. In Ahmadi et al the ring prosthesis frame is a coiled spring ribbon which is adjusted by a mechanical screw assembly. In Angell, a drawstring is used to adjust the circumference of a rigid frame member. Again, these ring prosthesis suffer from the disadvantages of the rigid ring prosthesis discussed above.
A further disadvantage with the Angell prosthesis relates to the design of the adJusting mechanism. The Angell prosthesis includes a rigid partial annular member. The open end of this member forms a gap which can be narrowed by tightening the drawstring. The tighter the drawstring is pulled the narrower the gap. The stress applied to the ring prosthesis during the opening and closing of the valve is primarily directed to the drawstring. Thus failure of the drawstring allows the prosthesis annulus to expand, allowing the valve to dilate.
It would thus be advantageous to design an annuloplasty ring prosthesis having an annular frame member which more closely reflects the naturally flexibility of the valve annulus, while providing for a sufficient degree of rigidity to resist dilation of the valve during the cardiac cycle.
An annuloplasty ring prosthesis which was designed in an attempt to provide for an elasticity closely resembling that of a natural heart valve is taught in U.S. Pat. No. 4,055,861, issued to Carpentier on Nov. 1, 1977. The annuloplasty ring prosthesis taught in Carpentier is described as being deformable, to an equal degree and simultaneously in all directions within and outside its resting plane, so as to form a skew curve. The preferred support is described as having the elasticity of an annular bundle of 2 to 8 turns of a cylindrical bristle of poly(ethylene terephthalate). In describing the support the individual bristles may either be interwoven, or merely arranged in a side by side relationship. The extremities of the individual bristles are joined together by welding, gluing with an adhesive or ligation.
The resulting ring prosthesis of Carpentier '861 will have a single degree of flexibility, which is dependent upon the flexibility of the individual bristles, and/or the number of these individual bristles used to construct the support. Thus this device will either be rigid or completely flexible, in either case such a ring prosthesis would have the disadvantages associated with such types of ring prosthesis.
It would thus be desirable to provide a ring prosthesis which provides for a more natural flexibility of the valve annulus without suffering the above discussed disadvantages.